The "Install system libraries" step was stalling indefinitely. It was not deadlocked on a config prompt and not slow-but-progressing: measured inside the live runner container, /var/cache/apt/archives stayed at 0 .deb files after 3+ minutes, with apt's http workers parked in S state waiting on the network. Root cause is the http:// mirror path being pathologically slow from this runner, not broken. Measured 2026-08-04 from inside the CI container, same index file, back to back: http://archive.ubuntu.com/ubuntu/dists/noble/Release 20.1s https://archive.ubuntu.com/ubuntu/dists/noble/Release 3.1s apt fetches many indexes serially, so ~20s apiece compounds into what looks like a hang. Rewriting the deb822 sources to https makes the step complete. Verified before committing, in the running CI container (rocker/r-ver:4.4): - ca-certificates present and apt 2.8.3 ships the https method built in, so nothing has to be installed over http first to bootstrap TLS - the sed rewrites both URIs (archive + security); the only remaining http:// is an inert comment line - '#' is used as the sed delimiter deliberately: '|' collides with the alternation and fails with "unknown option to `s'" - the regex survives YAML block-scalar parsing with backslashes intact `|| true` guards each sed because the step runs under `sh -e`, so a missing-sources-file on some other base image must not kill the job.